1. Field of the Invention
The present invention is directed to a structure of a display device for preventing electromagnetic interference (EMI). The display device comprises a display panel with a plurality of pixels formed between substrates.
2. Background of the Invention
Many conventional display devices such as a plasma display device and others employ an electromagnetic shield as a measure against EMI so that an electromagnetic wave generated by the display devices would not have an undesirable effect on various adjacent control circuits or communication systems.
FIG. 16 shows a sectional structure of a display device 100 comprising such a display panel. One example of a display panel 10 (hereinafter referred to as a panel) is an AC type plasma display panel (PDP). As shown in FIG. 16, in order to electromagnetically shield the display device 100, the panel 10 and a drive circuit substrate 12 equipped with a drive circuit for driving the panel 10 are disposed within a conductive shielding case 20 made of metal. In the conductive shielding case 20, a holding board 15 is provided on a non-display surface side of the panel 10 (below the broken line in the figure), which is opposed to a display surface 10a, to hold the panel 10 made of a glass substrate or the like. The panel 10 and the drive circuit substrate 12 are connected by a wiring board 14 including signal wiring, such as a flexible printed circuit (FPC). The wiring board 14 is also deposited within the conductive shielding case 20.
If the conductive shielding case 20 totally covers the whole surfaces of the panel 10 and the drive circuit substrate 12 which is the biggest source of noise, a reliable electromagnetic shield becomes possible. In the display device as shown in FIG. 16, however, the conductive shielding case 20 does not cover the display surface of the panel 10 which is thus covered by a transparent or translucent conductive filter 18 to be electrically connected to the conductive shielding case 20. By surrounding the panel 10 and the drive circuit substrate 12 with the conductive shielding case 20 and the conductive filter 18, an electromagnetic noise emitted outside the display device 100 is excluded.
Employed as the conductive filter 18 for covering the display surface of the panel 10 is, for example, a glass or acrylic filter with a transparent conductive film, such as an indium tin oxide (ITO) film or a considerably thin silver evaporation film, formed on the internal or external surface thereof, or a filter with fine conducting wires formed lengthwise and crosswise with a small pitch, that is, a filter with a fine wire gauze laminated thereto.
Though conductive, the transparent conductive film such as an ITO has a higher electrical resistance compared to a metal material such as the conductive shielding case 20, thereby providing less shield effect. Thus, in order to reduce the electrical resistance and increase the shield effect, the transparent conductive film needs to be thicker. However, the increased film thickness of the transparent conductive film deteriorates transmittance of light. This reduces display brightness or contrast, thereby reducing display quality. Further, it takes time and increases manufacturing cost to form a thick transparent conductive film.
The fine wire gauze, on the other hand, causes low transmittance of light, and in some cases, generates moire' on the display surface side in relation to a dot pitch of each pixel of the panel 10. Thus, in this case, it is difficult to prevent deterioration in display quality.